Actually, nuptial is a perfectly valid and commonly used word.
In Hebrew there are many words that don't have a singular form. For example מים (water) and פנים (face). But in English there are certainly some words that signify a single object but are pluralized, such as "pants" and "eyeglasses"/"spectacles". With respect to this particular word, first off, the suffix ן instead of ם has to do with the Aramaic origin of the word. I suspect that the word has a plural sense because in Jewish tradition it specifically encompasses quite a few different components of the marriage process.
Here's an interesting article I found on the subject: (it's in Hebrew, great practice) http://goo.gl/1wmEZA
In the English I have heard spoken in the northwestern, northeastern, and north central parts of the United States, one does not hear the singular noun "nuptial." The adjective "nuptial" is heard, as in "nuptial blessing," and the plural "nuptials" is applied to weddings, but the singular noun is not. "Nuptials" is, of course, simply a substantivized adjective, and I suspect that "nuptial" as a singular noun might at one time have been used for a nuptial mass, but we now only use it in the plural form, I assume originally referring to all the events having to do with the wedding.
Well, not formally. But it can be clear from the context (אֲנִי דּוֹרֵשׁ נִשּׂוּאֵי־יִתְרוֹן לִשְׁתֵּי בָּנוֹת שֶׁלִּי I require advantageous marriages for my two daughters) or made clear by attached pluralic attributes (אֲנִי נִכְשַׁ֫לְתִּי בִּשְׂנֵי נִשּׂוּאִים I failed in two marriages or לְמַעֲשֶׂה רוֹב הַנִשּׂוּאִים שֶׁאֲנִי מַכִּיר הֵם נוֹרָאִים in fact, most marriages I know are terrible).
Well, originally the word is derived from the expression נָשָׂא אִשָּׁה, when you (as a man) take the bride into your household, which is different from the אֵרוּסִין betrothal (also a plural noun), which takes place some time earlier (with a virgin usually a year earlier). In my prosaic thinking I subsumed it into the category of abstract plurals like נְעוּרִים youth, סַנְוֵרִים blindness and בְּתוּלִים virginity, but maybe you can come up with a better explanation for these plurals used in judicalese terms.
This is awkward in English because נישואין is plural and דבר is singular. In English, these would be expected to match: Marriages are serious things, or Marriage is a serious thing. I'll bet this question scores a very high percentage of wrong translations because of this.
I don't understand this. Hebrew requires tense and number (singular/plural) to match, and נישואין seems female plural, הם for a single item (not mixed group) means male plural, and דבר is non-gender singular. How is this grammatically correct? Why not הן? Why not נישואים? Why not דברים?
Well, נִשּׂוּאִין is an Aramaic plural and indeed masculine. The Hebraized spelling would be נִשּׂוּאִים. I suppose, the word "marriage" was used much in Rabbinic writings, where Aramaic expressions abound, and so this form was retained in Modern Hebrew too. As "marriage" is a plurale tantum, i.e. technically a plural form for a single thing, you may call it a דָּבָר, like English "Scissors are a good thing to have handy."
the hebrew word for marriage is a singular noun. Why then is the pleural pronoun used, when it seems a singular pronoun should be used. Even more complicated, is that the adjective for "serious" is written in the singular. Marriage should be either singular or pleural, it can't be both.
Well, the word נִשּׂוּאִין is an Aramaic plural and used as the subject. The predicate is the singualar noun דָּבָר. You can combine a plurale tantum (a word which is formally plural, but expresses a singular thing) with a noun in the singular, consider English: Scissors are a good thing to have handy.